Newlin,
I might get more feedback if you relist your post in the 911 Technical Forum or the 911 Engine Building Forum.....you'll definitely get told to drop in a 3.0/3.2/3.3/3.4/3.6/3.8 TURBO motor from us here!
That being said, my vote goes to rebuilding what you have and then going with carbs/pmo's or individual stack injectors(EFI), headers and muffler. A friend of mine just did his SC with NOS Webers on PMO runners, SSI headers and M&K Muffler and it is a thing of beauty. Goes pretty good too.